Cable modem optimized for high-speed data transmission from the home to the cable head

ABSTRACT

A cable modem provides upstream data signals in a cable system on a return channel. The upstream data signals are provided in a 50-550 MHz frequency range and yet do not affect the picture quality associated with conventional cable television signals. The data is provided on vestigial sidebands associated with the cable television signals or during black periods associated with the cable television signals. The data can be modulated in accordance with quadrature amplitude modulation (QAM) techniques.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of Ser. No. 08/990,279, filedDec. 15, 1997, now U.S. Pat. No. 5,986,691 which was granted on Nov. 16,1999.

FIELD OF THE INVENTION

The present invention relates to cable communication systems. Moreparticularly, the present invention relates to high-speed transmissionof data from a home or residence to a central office or cable-head end.

BACKGROUND OF THE INVENTION

Conventional cable systems can utilize a cable modem to transmit and toreceive data across a coaxial cable or line. The cable couples a headend or central office to numerous pieces of video equipment disposed ina multitude of residences.

Cable systems are generally utilized as one-way systems in which cabletelevision signals are transmitted from the head end to the videoequipment coupled to the cable. The video equipment can include videocassette recorders (VCRs), television units, or other devices. The cabletelevision signals are transmitted in a frequency range fromapproximately 50 megahertz (MHz) to 550 MHz. The video equipmentreceives the cable television signals and either provides images inaccordance with the cable television signals or stores the cabletelevision signals.

Cable modems can be utilized with existing cable systems to communicatedata bidirectionally between the home and the head end. The cable modemtransmits data from the home to the head end in a frequency rangebetween approximately 5-39/42 (e.g., on a return channel). Generally,the return channel can utilize a 5-39 MHz range (low split) or a 5-42MHz range (mid split). The cable modem receives data from the head endin a frequency range between 550-750 MHz (e.g., the downstream channel).The high-speed, downstream channel is often utilized to providedigitized services, such as, digitized entertainment to the residence,or to provide other data communications to the residence.

The return channel is typically utilized to transmit small amounts ofdata, such as, requests for download information, while the downstreamchannel is utilized to transmit large amounts of data, such as, dataassociated with video signals, large programs, documents, or otherapplications. For example, in most internet applications, larger amountsof data are requested by the residential user than by the internetsource. Further, in pay-per-view movie applications, the return channelis utilized to transmit relatively small data files, including billingand addressing information, while the downstream channel is utilized totransmit the relatively large data file, including the movie.

The conventional return channel is not adequate for all cable modemapplications, especially applications in which larger amounts of datamust be transmitted to the head end. Heretofore, the return channelassociated with conventional cable modems can be susceptible tointerference from a number of other radio frequency (RF) sources,including amateur radio units and household motors, which providedistortion in the 5-39/42 MHz range. Additionally, the bandwidthassociated with the conventional return channel (e.g., 5-39/42 MHz) issomewhat limited, thereby restricting the amount of data which can besent to the head end.

Since the frequency range between 50-550 MHz is utilized by alltelevision sets coupled to the cable, it cannot conventionally be usedfor return channel applications. Indeed, the reception of all televisionsets would be affected by any signal placed in the frequency bandbetween 50-550 MHz. Accordingly, conventional cable modems must transmitand receive data outside of the 50-550 MHz range to protect thereception of the large number of customers who are already committed tothis aspect of the cable system. Thus, data cannot normally betransmitted upstream in the 50-550 MHz frequency range because of themulti-drop nature of the cable system.

Thus, there is a need for a high-speed return channel for cable modems.Further still, there is a need for more efficient use of the frequencyband between 50-550 MHz in a cable system.

SUMMARY OF THE INVENTION

The present invention relates to a transmitter for use with a cablesystem including a cable. The cable is coupled between the transmitterand a cable-head end. The transmitter includes a terminal and a datamodulator coupled to the terminal. The data modulator provides modulateddata signals in a frequency band between 50-550 MHz across the cable,wherein the modulated data signals are transmitted so as not tointerfere with reception of cable television signals.

The present invention further relates to a cable modem including areceiver means and a transmitter means. The receiver means receivesanalog television signals in a frequency range between 50-550 MHz. Thetransmitter means transmits data signals on a vestigial sideband ofcarrier waves between the 50-550 MHz frequency range. The transmissionof the data signals does not adversely affect the picture qualityassociated with the analog television signals.

The present invention still further relates to a transmitter for use ina cable system. The transmitter provides data signals between 50-550 MHzon a return channel to a cable-head end. The transmission of the datasignals does not adversely affect the picture quality associated withanalog television signals in the 50-550 MHz frequency range.

According to one exemplary aspect of the present invention, a cablemodem provides data signals outside of the conventional return channelfrequency range between 5-39/42 MHz. The return channel utilizes a blackperiod associated with cable television signals or a vestigial sidebandassociated with cable television signals to transmit data in the 50-550MHz frequency range. The return channel advantageously does notadversely affect the reception of cable television signals in the 50-550MHz frequency range.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will hereafter be described with reference to theaccompanying drawings, wherein like numerals denote like elements and:

FIG. 1 is an exemplary block diagram of a cable system;

FIG. 2 is a general block diagram of a cable modem for use with thecable system illustrated in FIG. 1 in accordance with an exemplaryembodiment of the present invention;

FIG. 3 is a drawing of the bandwidth spectrum of a television channelshowing a vestigial sideband;

FIG. 4 is a more detailed block diagram of the cable modem illustratedin FIG. 2; and

FIG. 5 is a general block diagram of a cable modem for use with thecable system illustrated in FIG. 1 in accordance with another exemplaryembodiment of the present invention.

DETAILED DESCRIPTION OF PREFERRED EXEMPLARY EMBODIMENTS

With reference to FIG. 1, a cable system 12 includes central office or ahead end 14, a fiber optic cable 16, a fiber node 18, a coaxial cable20, and a multitude of residences 22. Cable 20 is preferably aninsulated coaxial cable of the type utilized by cable systems whichprovide cable television signals to residences 22. Fiber optic cable 16couples head end 14 to fiber node 18. Fiber node 18 is coupled to cable20.

Head end 14 can also be coupled to a satellite cable television antenna28, an asynchronous transfer mode (ATM) network 30, a public switchedtelephone network (PSTN) 32, or other services. Head end 14 transmitsand receives signals to antenna 28, network 30, and network 32. Head end14 preferably receives cable television signals from antenna 28 andprovides cable television signals across fiber optic cable 16 to fibernode 18. Fiber node 18 provides the cable television signal across cable20 to residences 22. The cable television signals are analog signalswithin a frequency range approximately between 50-550 MHz.

Additionally, head end 14 can receive cable television signals fromnetworks 30 or 32. Head end 14 can also receive data from network 30 and32 and provide the data across cables 16 and 20 to residences 22. Thedata can include digitized services, digital entertainment, pay-per-viewmovies, or other information. For example, ATM network 30 can be coupledto the internet or worldwide web and information can be transmitted toand from the internet or worldwide web via cable 20 and cable 16.

With reference to FIGS. 1 and 2, a cable modem 50 can be utilized insystem 12 to communicate information across cable 20. Preferably, cablemodem 50 is provided within residences 22. Cable modem 50 includes adata input 52, a data output 54, a modulator 56, a demodulator 58, and aterminal 60. Terminal 60 is a terminal preferably coupled to cable 20.

Cable modem 50 advantageously transmits data or digital informationupstream (e.g., from residence 22 to head end 14) in the frequency rangeapproximately between 50-550 MHz. In contrast to conventional modemswhich utilize a return channel in the frequency range betweenapproximately 1-50 MHz, cable modem 50 utilizes the same frequency rangefor the return channel that is used for the cable television signalsprovided from head end 14 to residences 22. Data or digital information(e.g., modulated data signals) received by modem 50 from head end 14across cable 20 is provided through demodulator 58 to output 54. Thereceived data is preferably provided in the 550-750 MHz frequency range(e.g., on the downstream channel).

Cable modem 50 is advantageously arranged so modulated data signalstransmitted within the 50-550 MHz frequency range do not interfere withthe picture quality associated with the cable television signals.Preferably, cable modem 50 includes a modulator, such as, modulator 56,which is configured so that the picture quality associated with thecable television signals received by residences 22 is not affected bydata transmitted upstream along cable 20. Preferably, modulator 56 isarranged as a vestigial sideband modulator.

With reference to FIG. 3, an exemplary bandwidth spectrum of a cabletelevision signal 80 is shown. Cable television signal 80 has abandwidth of 6 MHz and is within the 50-550 MHz frequency range. The 6MHz bandwidth represents a television channel.

A picture carrier frequency 82 is provided approximately 1.25 MHz from astarting frequency 84 associated with the channel. Informationindicative of the picture associated with cable television signal 80 ismodulated using a single sideband technique, wherein the pictureinformation is contained between picture carrier frequency 82 and afrequency approximately 5.75 MHz above starting frequency 84. At afrequency 86, sound information can also be provided.

Cable television signal 80 is transmitted utilizing a single sidebandtechnique, wherein only one sideband contributes to the recovery of theinformation encoded on the cable television signal. Modulator 56 (FIG.2) preferably utilizes a vestigial sideband 92 associated with cabletelevision signal 80. Vestigial sideband 92 is in a frequency rangebetween 0.5-1.25 MHz above frequency 84. Vestigial sideband 92preferably has a bandwidth of 0.75 MHz and does not interfere with othertelevision channels since it is greater than frequency 84. Additionally,vestigial sideband 92 should not interfere with its own channelassociated with signal 80 because it is below carrier frequency 82.

Modulator 56 (FIG. 2) preferably utilizes quadrature amplitudemodulation (QAM) to provide modulation in vestigial sideband 92.Alternatively, modulator 56 could utilize phase shift key (PSK)modulation, frequency shift key modulation (FSK) or other types ofmodulation. Therefore, modem 50 (FIG. 2) is able to utilize the 50-550MHz frequency range to transmit information upstream on cable 20 byutilizing vestigial sideband 92. Utilizing the vestigial sideband willnot provide an adverse effect on picture quality associated with cabletelevision signal 80. Modem 50 can use a vestigial sideband similar tosideband 92 on any channel between the 50-550 MHz frequency range.Withreference to FIG. 4, modem 50 includes a transmitter 100, a receiver102, and a hybrid circuit 128. Transmitter 100 includes a band passfilter 104 and modulator 56. Receiver 102 includes a band pass filter106 and demodulator 58. Modulator 56 is a QAM modulator and includes ascrambler 110, a bit-to-symbol mapper 112, an in-phase pulse generator114, a quadrature pulse generator 116, a base band transmit filter 118,a base band transmit filter 120, a mixer 122, a mixer 124, and a summer126.

Data is provided at input 52 through self-synchronizing scrambler 110.The scrambled data is provided to bit-to-symbol mapper 112, whichprovides symbols to pulse generators 114 and 116. Pulse generators 114and 116 provide quadrature pulse signals through base band transmitfilters 118 and 120, respectively, to mixers 122 and 124. Mixers 122 and124 provide up-converted signals to summer 126. Mixers 122 and 124provide the up-converted signals in a vestigial sideband, such as,sideband 92. Summer 126 provides the modulated data signals (e.g., thesummed, up-converted signals) in a vestigial sideband associated withcable television signals provided on cable 20.

The modulated data signals are provided through band pass filter 104 andthen hybrid circuit 128 to cable 20. Signals received on cable 20 areprovided through hybrid circuit 128 and band pass filter 106 todemodulator 58.

Demodulator 58 includes a mixer 130, a mixer 132, an in-phase equalizerfilter 134, a quadrature equalizer filter 136, a slicer 138, asymbol-to-bit map 140, and an unscrambler 142. The modulated datasignals are provided to mixers 130 and 132 and are down-converted. Thedown-converted signals are provided through equalizers 134 and 136 toslicer 138. Slicer 138 provides symbols representative of the modulatedsignals to symbol-to-bit mapper 140. Symbol-to-bit mapper 140 providesbit signals to unscrambler 142, which provides unscrambled data atoutput 54. The modulated data signals provided to mixers 130 and 132 arein the 550-750 MHz frequency range.

With reference to FIG. 5, a cable modem 250 in accordance with anotherexemplary embodiment, is shown. Cable modem 250 is similar to modem 50.However, cable modem 250 includes a black region modulator 256 insteadof a vestigial sideband modulator 56. Modem 250, like modem 50, providesmodulated data signals to cable 56 in the 50-550 MHz frequency bandwithout interfering with the picture quality associated with the cabletelevision signals.

Black region modulator 256 is coupled to a timing reference circuit 258,which is also coupled to terminal 60. Timing reference circuit 258determines the black signal time periods associated with channels on thecable television signals. Black signal time periods are time periodswhen no information is provided on the cable television signal toaccommodate a retrace operation associated with the cathode ray tube(CRT). During a retrace orientation, the cable television signal turnsoff the electron beam associated with the CRT so the retrace operationcannot be seen by the viewer.

The retrace operation can occur at the end of a horizontal trace or scanof the electron beam. At the end of the horizontal trace, the electronbeam must fly back and start a next horizontal trace. A retraceoperation can also occur when the scan reaches the bottom of the screenassociated with the CRT, and the electron beam has to come back to thetop of the screen. During these retrace time periods, the cabletelevision signal is driven into a black region, which essentially turnsoff a transmission of the electron beam so the retrace operation cannotbe seen on the screen.

Black signal modulator 256 is optimized to operate during the retracetime period to provide modulated data signals. The modulated datasignals do not affect the cable television signals because they areoccurring during retrace or flyback times (e.g., black regions of thecable television signals). The cable television signals are over-drivenduring the black regions so that the electron beam is totally turnedoff. Although the signal is over-driven, data still can be modulated ontop of the over-driven signal. The data can be modulated with QAM, FSK,PSK, or other techniques. The use of black periods to include data hasbeen utilized in other non-cable modem applications by companies, suchas, “Datacast”, to transmit data from a central source to computers at arelatively high rate.

With reference to FIG. 1, modems in head end 14 or fiber node 18 canutilize echo-canceling techniques to remove the transmitted cabletelevision signals between 50-550 MHz frequency range to obtain themodulated information, whether it be on a vestigial sideband or in ablack region of the cable television signals. Echo-canceling techniquesused in order to transmit and to receive data on a single medium, arewell-known in the art.

It is understood that, while the detailed drawings and specific examplesgiven describe preferred exemplary embodiments of the present invention,they are for the purpose of illustration only. The method and apparatusof the present invention is not limited to the precise details andconditions disclosed. For example, although particular modulation anddemodulation circuitry is described, other types of modulation anddemodulation techniques can be utilized. In addition, modem 50 can beconfigured to utilize both the black region and the vestigial sideband,as well as, transmit in the 5-39/42 MHz frequency range, therebymaximizing the amount of data which can be transferred. Further, singlelines in the drawings can represent multiple conductors. Thus, changesmay be made to the details disclosed, without departing from the spiritof the invention defined by the following claims.

What is claimed is:
 1. A transmitter for use with a cable systemincluding a cable, the cable being coupled between the transmitter and acable-head end, the cable system transmitting cable signals on channelshaving a first bandwidth, wherein the cable signals are modulated in asecond bandwidth, the second bandwidth being less than the firstbandwidth, the transmitter comprising: a terminal; and a data modulatorcoupled to the terminal, the data modulator providing modulated datasignals in a frequency band within one of the channels, wherein themodulated signals are provided in a third bandwidth within the firstbandwidth and exclusive of the second bandwidth.
 2. The transmitter ofclaim 1, wherein the cable is a coaxial cable.
 3. A transmitter for usein a cable system, the cable system providing cable television signalson channels, each channel including a television signal bandwidth and areturn bandwidth, the return bandwidth being exclusive of the televisionsignal bandwidth, the transmitter providing data signals between 50-550MHz in the return bandwidth of one of the channels, wherein transmissionof the data signals does not adversely affect the picture qualityassociated with the cable television signals.
 4. The transmitter ofclaim 3, wherein the cable is a coaxial cable.
 5. The transmitter ofclaim 1, wherein the data modulator includes a scambler.
 6. Thetransmitter of claim 1, wherein the data modulator utilizes quadratureamplitude modulation to provide modulation of data signals.
 7. Thetransmitter of claim 1, wherein the data modulator utilizes frequencyshift key modulation to provide modulation of data signals.
 8. Thetransmitter of claim 3, wherein the data signals provided by thetransmitter are modulated.
 9. The transmitter of claim 3, wherein thedata signals are transmitted to an asynchronous transfer mode (ATM)network.
 10. The transmitter of claim 3, wherein the data signalsinclude requests for particular analog television signals.
 11. Thetransmitter of claim 3, wherein the data signals include requestsassociated with internet web pages.
 12. A method of communicating highspeed data transmissions and cable television over a common line at acommon frequency range, the method comprising: transmitting cabletelevision signals from a head end to a subscriber end on channels, thecable television signals being located within channels, each of thechannels having a first bandwidth the cable television signals beingwithin a second bandwidth within the first bandwidth; and transmittingdata signals from the subscriber end to the head end the data signalsbeing located within a third bandwidth within the first bandwidth of thechannels, the second bandwidth being exclusive of the third bandwidth ineach of the channels.
 13. The method of claim 12, wherein the step oftransmitting data signals utilizes a vestigial sideband.
 14. The methodof claim 12, further comprising transmitting data signals from the headend to the subscriber end.
 15. The method of claim 12, wherein the datasignals do not interfere with television signals.
 16. The method ofclaim 5 wherein the step of transmitting the data signals utilizeschannels between 50-550 MHz.
 17. The method of claim 12, wherein thestep of transmitting cable television signals comprises utilizing asingle sideband technique, wherein only one sideband contributes to therecovery of the information encoded on the cable television signal. 18.The method of claim 12, wherein the third bandwidth is less than 0.75MHz.
 19. The method of claim 12, further comprising a step of removingtransmitted cable television signals utilizing echo-cancelingtechniques.
 20. The method of claim 12, wherein the step of transmittingdata signals occurs simultaneously with the step of transmitting cabletelevision signals.